PWM CONTROL FOR HYBRID CLAMPED MULTILEVEL INVERTERS

Abstract

A hybrid clamped multilevel inverter topology comprising active and passive clamping devices is presented in this paper. In this topology, the dc-link capacitor voltages can be balanced without additional circuitry or separated dc voltage sources, regardless of load characteristics. It can be used in real and reactive power conversion applications. The topology structure, operating principle and self-voltage balancing ability are analyzed. The PWM control method called higher and lower carrier cells alternative phase opposition PWM (HLCCAPOPWM) is employed for the hybrid-clamped multilevel inverter and it is based on the improvement of carrier phase disposition PWM (PDPWM). This method can effectively reduce the number of devices switching on or off within broad modulation index range, consequently reducing switching losses, and remarkably reduce the amplitude of lower harmonics. Simulation results of five-level inverter are also presented.